1. Field of the Invention
The present invention relates in general to a system and method for correcting beam exposure during beam shaping and/or beam positioning. It more particularly relates to a method and apparatus for correcting the exposure of a particle beam such as a particle or other beam for use in various applications such as particle beam lithography.
2. Background Art
There is no admission that the background art disclosed in this section legally constitutes prior art.
A typical particle beam lithography device may include a beam column having a series of high speed deflectors. The top set of deflectors is referred to as a blanker and turns on and turns off the beam. The other deflectors may be beam shape deflectors and position deflectors.
The shape deflectors position the beam over a cutting aperture to generate different sizes and shapes of the beam, such as rectangles, triangles, etc. The voltage applied to the shape deflectors may be dependent on the desired size and shape of the beam. The beam column may contain more than one set of shape deflectors and cutting apertures.
The position deflectors such as raster scan and/or vector scan deflectors may position the beam by, for example, applying a directional vector to the shaped beam. The voltage values to the vector deflectors may be different for each different directional vector. Therefore the voltage values to these vector deflectors may be changing for each flash of the beam. Similarly, the beam column may contain more than one set of raster scan and/or vector deflectors.
The lithography device further may include a controller for providing deflector voltages to these deflectors. The controller may include, for example, a digital board having a field programmable gate array (FPGA). The FPGA receives the shape and directional vector codes and converts them into digital words that represent the voltage values for the deflectors. These digital words may be provided to digital to analog converters (DACs). These DACs may include output amplifiers having high slew rates causing significant ringing of the deflector voltage waveform.
The flash rate and lithography accuracy requirements for the next generation beam lithography are much greater than those of previous shaped beam tools. Nominally, shape size and placement accuracy of 1 part in 4000 (or 0.025%) are required. Typically, the raw accuracy of high speed output driven over several feet of cable to an imperfectly terminated deflector may be a few parts per hundred.
To achieve high writing throughput (i.e. high flash rate), it is necessary for at least some applications to unblank the beam before the shape and vector deflection signals have fully settled to their final values. Due to the high rate of the output amplifier and imperfections in the electronics, the settling time may be longer than the blanking time causing the actual deflector voltage to exhibit significant oscillation or ringing.
In the case of the vector deflection signals, this has the effect of causing the exposed flash to “move around” slightly. The position at which the edge resolves is a function of the average deflection voltage during the exposure time of the flash. The ringing may affect the average deflection voltage during the exposure time by causing a blurring of the doping of the resist at the edge of the desired pattern or shape. This blurring may cause a displacement of the dose development threshold on the resist, resulting in an offset position of the shape of the resist. The blur caused by this motion cannot be eliminated in many instances.
A problem can exist when increasing the flash rate to achieve the shape size and placement accuracy required for this generation of beam lithography devices due to the ringing of the deflector voltage signals. A technique is needed for modern high speed, high accuracy beam systems to correct for the ringing of the deflector voltage signals.